1. Field of the Invention
The present invention relates to a coaxial type starter device, and more particularly to a coaxial device for starting the engine of a vehicle and using an improved over-running clutch device.
2. Prior Art
The conventionally used starter device for starting the engine of a vehicle is a so-called a two-shaft structure, wherein an electromagnetic device for energizing a DC motor is arranged on a side of the DC motor. However, such a two-shaft type starter device imparts a great restriction to a layout of the engine when a vehicle is designed. Therefore, a proposal has been made in which an electromagnetic switching device is arranged on one end in an axial direction of a DC motor, so that the starter device can be formed into a simple configuration such as a mere elongated tubular body.
According to the aforementioned proposal, a coaxial type starter device using an overrunning clutch device as shown in FIG. 6 has been designed. This coaxial type starter device 1 is constructed in such a manner that an armature rotational shaft 3 of a DC motor 2 is made to be hollow, a plunger rod 4a of an electromagnetic switching device 4 arranged at the rear end of the DC motor 2 is inserted into an internal passage 3a of the armature rotational shaft 3, and the rod 4a is brought into contact with the rear end of an output rotational shaft 5 which is arranged coaxially with the armature rotational shaft 3 and having the rear end thereof inserted into the internal passage 3a so that the output rotational shaft 5 may be forwardly forced out.
In such a coaxial type starter device 1, the rotational of the armature rotational shaft 3 is reduced in speed by means of a planet gear unit 6, comprising a sun gear 6a meshed with a plurality of planet gears 6b which are further meshed with an internal gear 6c provided on the inner peripheral surface of a frame 9 and also supported on a carrier 6e through shafts 6d. The reduced rotation is further transmitted to the output rotational shaft 5 through an overrunning clutch device 7 to rotate a pinion 8 mounted on the front end of the output rotational shaft 5. The conventional overrunning clutch device 7 is provided with a clutch outer or race 7a rotated by the reduced turning force, and a plurality of cam surfaces are formed at equal intervals in the inner peripheral surface of the clutch outer 7a, which cooperates with the outer peripheral surface of a tubular clutch inner or race 7b arranged internally of the clutch outer 7a to define wedge-shaped spaces. A roller 7c is arranged in each wedge-shaped space so that when the clutch outer 7a is rotated in a predetermined direction, the roller 7c rolls into frictional engagement with the cam surface, whereby the clutch inner 7b is connected to the clutch outer 7a and the rotation is transmitted.
The output rotational shaft 5 is inserted internally of the clutch inner 7b whose inner peripheral surface is provided with a helical spline 7d formed along the rotational direction of the output rotational shaft 5 so as to be meshed with a spline forming portion 5a having a larger outside diameter than the inside diameter of the internal passage 3a of the armature rotational shaft 3. Thereby the output rotational shaft 5 can receive the turning force from the clutch inner 7b, and a pinion 8 at the front end portion of the output rotational shaft 5 activates the ring gear of the engine to rotate when the output rotational shaft 5 is moved in an axial direction thereof.
In such an overrunning clutch device 7, in starting the engine, when the output rotational shaft 5 is conversely rotated at high speed by the engine, the clutch inner 7b is rotated at higher speed than the clutch outer 7a, and therefore, the frictional engagement thereof with the clutch outer 7a by way of the roller 7c is released to cut off the reverse transmission to the clutch outer 7a.
The conventional overrunning clutch device 7 having been designed as described above poses a problem in that when the output rotational shaft 5 receives a high load including shocks produced due to a change in pulse-like load generated when the pinion 8 is thrust into engagement with a rotating ring gear, for example, when starter device is actuated when the engine already operating, the ring gear as well as various components are liable to be damaged since such load is only absorbed as a distorted energy generated by a torsion rigidity produced through the above clutch inner, clutch outer and the roller.